Snap-in plunger switch



March 9, 1965 F. A. ZODA SNAP-IN PLUNGER SWITCH 2 Sheets-Sheet 1 FiledOct. 9, 1961 FZEDEQJCK A. ZooA ATTORNEY March 9, 1965 F. A. ZODA SNAP-INPLUNGER SWITCH 2 Sheets-Sheet 2 Filed Got. 9, 1961 A w m1 mA K m 2 E D aF ATTORNEY United States Patent 3,172,9ss SNAP-IN PLUNGER SWITCHFrederick A. Zoda, Trenton, N..I., assignor to Circle F Mfg. (10.,Trenton, N.J., a corporation of New Jersey Filed Oct. 9, 1961, Ser. No.143,878 6 Claims. (Ci. 290-168) This invention relates generally toeectrical wiring devices. More particularly, the invention has referenceto a switch adapted for mounting in refrigerators, ovens, automobiles,or other environments in which the switch is to be operated by theclosing and opening of a door. A switch of this type is known to thetrade as a plunger switch. Most usually, the switch is normally on,although in some applications the switch may be normally oif when theplunger is in its extended position.

Comparatively recently, switches of this type have been designed toinclude snap-in means, whereby the switch is adapted to be quicklyinstalled in an opening provided in the panel of the refrigerator orother structure in which it is to be used. The snap-in means found mostsuitable for this purpose conventionally embodies a switch cover formedat its periphery with an annular series of spring fingers. Such anarrangement facilities to a marked degree the assembly of the switchesin the associated supporting structures, inasmuch as the two conductorsintended for attachment to the switches can be drawn through themounting hole of the associated support structure, and secured to theterminals of the switch, after which the switch is merely pressed intothe mounting hole from the front to complete the installation.

In the highly competitive field in which switches of this category fall,it is of great importance to provide a switch having its molded and diemade parts reduced to a minimum, without sacrifice of the ability of theswitch to obtain a high electrical rating. The reduction of parts to aminimum, of course, not only reduces mold and die costs, but also,effects a continuous saving in assembly costs, throughout the time thatthe switch is manufactured.

The main object of the present invention is to achieve the abovementioned reduction of mold, die, and assembly costs, through theincorporation of novel features in the switch, such that variouscomponents of the switch are coactively related to impart theretoassembly functions not heretofore envisioned for said components by theindustry.

With further regard to the reduction of costs generally, another objectof the invention is to design individual components of the switch insuch a manner as to lower to a considerable extent the amount ofmaterial heretofore thought required for said components by the trade.

A further object is to provide a switch in which there will be maximumnormal projection of the plunger, when the door is opened, while yetobtaining minimum overall depth of the portion of the switch that isdisposed interiorly of the associated regfrigerator or other supportstructure. This is of importance, in that manufacturers of majorappliances such as refrigerators and ovens are continually endeavoringto effect reduction in wall thicknesses to obtain maximum capacity inrelation to the overall area of the appliance. In turn, this dictatesthe need for shallower wiring devices.

In the trade, it becomes important to provide maximum normal plungerprojection in relation to maximum travel of the plunger to a depressedposition. It is ordinarily required that the plunger be capable ofdepression through a position in which it is flush with the cover of theswitch, and obviously, it becomes difficult to achieve this, while atthe same time obtaining minimum depth of the installed switch andmaximum normal projection of the plunger. The present invention aims toprovide maximum plunger projection in relation to minimum overall depth,while still achieving the desired flush relation between the tip of theplunger and the cover of the switch in the depressed plunger position.

A further object is to provide a construction for the stationarycontacts of the switch, so designed as to provide for maximumcompactness of the switch while still achieving optimum electricalcharacteristics as regards the electrical valve at which the switch israted, the number of cycles through which the switch will ordinarilypass, etc.

Still another object is to provide, in a switch of this type, anarrangement wherein the exposed portions of the terminals will beseparated by a portion of the body of the device, which portion will beof substantial crosssection so as to provide an efiicient insulationbarrier between the terminals, with the terminals nevertheless beingconfined within the main circumference of the body.

Summarized briefly, the invention comprises a onepiece, molded body of aphenolic or other suitable dielectric material, forrned open at one endand having its other end reduced in cross-section so as to definediametrically opposed recesses receiving terminals projecting out of thebody. The reduced portion of the body comprises an insulation barrierfor the terminals, which are adapted to be constructed of relativelyshort length as compared to those conventionally utilized in switches ofthis type. Closing the open end of the body is a metallic cover, whichmay be suitably finished to impart thereto an attractive,corrosion-resistant characteristic. The cover has the usual annularseries of spring fingers, but in accordance with the present invention aplurality of said fingers are bent inwardly into underlying engagementwith shoulders formed upon the body of the device, whereby to assemblethe cover with the body and thus hold all the parts of the switch inassembled relation. The device is further provided with a plungerprojecting through a central aperture of the cover, said plunger havingat its inner end a rounded surface engaging the central portion of themovable contact, which is thus adapted to have a floating orrockingmotion upon the plunger, permitting the movable contact to seatitself properly against cooperating surfaces of a pair of stationarycontacts integral with the above-mentioned terminals. Due to thisarrangement, a clean double break is achieved in the device, so as toimprove measurably the electrical characteristics thereof. The plungeris springbiased to its normal, extended position, and in accordance withthe invention, guide grooves are formed in the inner surface of thebody, for the purpose of preventing relative rotation of the movablecontact, plunger, and stationary contacts during the use of the device.

Other objects will appear from the following description, the claimsappended thereto, and from th annexed drawing, in which like referencecharacters designate like parts throughout the several views, andwherein:

FIGURE 1 is a front perspective view of a door switch according to thepresent invention;

FIGURE 2 is a rear perspective view thereof;

FIGURE 3 is an enlarged longitudinal sectional view through the switch,taken substantially on line 33 of FIGURE 1 with the plunger in itsnormal, extended position;

FIGURE 4 is a transverse sectional view on the same scale as FIGURE 3,taken substantially on line 4--4 of FIGURE 3;

FIGURE 5 is a transverse sectional view through the switch, on the samescale as FIGURE 3, taken substantially on line 5-5 of FIGURE 3;

FIGURE 6 is a longitudinal sectional view, on the 3 same scale as FIGURE3, taken substantially on line 66 on FIGURE 4, with the plungerextended;

FIGURE 7 is a view similar to FIGURE 6 in which the plunger has beenpartially depressed;

FIGURE 8 is a fragmentary longitudinal sectional view substantially online 88 of FIGURE 4, on the same scale as FIGURE 3;

FIGURE 9 is a fragmentary longitudinal sectional view on the same scaleas FIGURE 3, taken substantially on line 99 of FIGURE FIGURE 10 is anexploded perspective view, on a scale slightly larger than that ofFIGURE 1, showing the plunger, one of the stationary contacts, and themovable contact.

Referring to the drawing in detail, the door switch comprising thepresent invention includes a one-piece, molded body of phenolic or othersuitable dielectric material, formed open at its forward end and having,as shown to particular advantage in FIGURES 1 and 2, a forward endportion 12 of circular cross-section.

Body 10 is provided with a reduced rear end portion 14, which in thepreferred, illustrated embodiment extends for slightly more than halfthe overall length of the body. The reduced portion 14 definesdiametrically opposed longitudinal or side recesses 16, coextensive withthe rear end portion 14. Recesses 16, at the juncture between endportions 12, 14, have end walls 18.

Formed in the outer surface of the body 19 is a pair of diametricallyopposed longitudinal grooves 20, terminating at their front ends inclosely spaced relation to the forward extremity of the body. Theprovision of the grooves 26 defines, at the closed front ends of saidgrooves, shoulders 22, which as shown in FIGURE 9 are undercut, saidshoulders being engaged by inwardly bent fingers 24 of a snap-in covergenerally designated 26. The cover will be described in detailhereinafter.

The provision of the longitudinal grooves 20 further defines, atopposite sides of each shoulder 22, stop surfaces 28, so that onengagement of the fingers 24 against the shoulders 22 during theassembly of the switch, relative rotation of the body It) and cover 26will be prevented due to the fact that any tendency toward said relativerotation will be prevented by engagment of the stop surfaces against thefingers 24 (see FIGURES 2 and 5).

Formed in the respective end walls 18 of the diametrically opposed siderecesses 16 are slots 30 (see FIG- URES 2, 3, and 5), through which theterminals of the switch project in a manner to be discussed in furtherdetail hereinafter.

Referring now to FIGURES 4 and 8, I provide diametrically opposedguideways 32 lying chordally of the body, in parallel relation, as bestshown in FIGURE 4. Guideways 32 communicate with a center cavity 34extending the full length of the body, said cavity being of circularcross-section (see FIGURE 4), with the guideways communicating with thecavity through the medium of connecting passages 36.

. Angularly spaced from the connecting passages 36 a distance slightlyless than 90 degrees are longitudinal guide grooves 38 which, like thecavity 34, extend the full length of the body. Guide grooves 38 extendradially from the central cavity, in full communication therewith overthe entire length of the guide grooves.

Connecting the respective passages 36 with the guide grooves 38 adjacentthereto are depressions 40. These are extended from one end of therespective guideways (FIGURE 4), and are relatively narrow in relationto their depth (see FIGURE 8}.

A pair of like, oppositely arranged stationary contacts 42 are providedin the device, each of these including an elongated, flat body part 44terminating at its rear end in a bevelled, apertured terminal 46 of themale tab type adapted to receive a conventional push-on, femaleconnector, not shown, whereby wires, also not shown, can

be attached to the terminals. Obviously, although tabtype terminals areillustrated by way of example, said terminals might be of other shapes,according to the particular type of connection desired.

At its upper end, contact 42 is formed (see FIGURES 4 and 10) with anarm 48 extending at an obtuse angle to the plane of the body part,within the forward end portion of the body 10. Arm 48, at its free end,is integrally formed with a depending contact element 50 angleddownwardly outwardly in a direction from arm 48. Thus, when theoppositely arranged contacts are assembled in the body (see FIGURES 6and 7), they diverge in a direction rearwardly from the front end of thebody, lying in planes oblique to the axis of the body, within the upperends of the guide grooves 38.

A compression, coil spring 52 seats on the rear end wall 53 of the body,and at its front end bears against the underside of a circular bodyportion of a movable contact generally designated 54.

The body portion of the movable contact has been designated 56, and isprovided with a central aperture surrounded by a forwardly projecting,low extrusion 58. Projecting radially from the periphery of the bottomportion are diametrically opposed, rearwardly divergent contact arms 60,the angle of which is selected to match that of the contact element 50,so that, as shown in FIGURE 6 to best advantage, there is a fullface-to-face contact between the contact arms 6! and the contactelements 50 in the on position of the switch.

A plunger 62 is of one-piece, molded construction, and like the body isof phenolic or other suitable dielectric material. Plunger 62 has, in apreferred embodiment of the invention, a rounded tip 64, and at the baseof the plunger there are formed diametrically opposed, Wide guide lugs66 (FIGURE 10). As shown to particular advantage in FIGURES 6 and 7, thebase end 68 of the plunger is convexly shaped, with the convexityextending about an elongated, axial bore 70 of the plunger, the bore 70communicating with a short counter-bore 72 at the base end of theplunger. Since the circular body portion 56 of the movable contact 54 iswholly planiform in the area thereof surrounding the extrusion, it willbe observed that the movable contact is engaged, in the normal positionof the parts, by the base of the plunger only in the areas of theplunger base and movable contact immediately bounding the counterbore 72and extrusion 58 respectively.

The extrusion, in this connection, is loosely positioned within thecounterbore, and it becomes apparent, therefore, that the movablecontact is imparted a self-seating floating characteristic such as topermit it to seat firmly against both of the contact elements 50 in fullface-toface engagement therewith, regardless of possible cocking of theplunger. This is of particular importance in a switch of this type, inview of the fact that the plunger is usually engaged and depressed by adoor that is turning about a hinge axis, thus causing the plunger to begiven a lateral pressure tending to tilt the same out of axial alignmentwith the remainder of the switch. Especially is this true when, as isoften the case, the switch is mounted in close proximity to the hingeaxis of the door.

The self-seating arrangement of the movable contact has further value,in that when the plunger is depressed by closure of the door, thecontact of the plunger with the movable contact is limited, ashereinbefore described, to the area immediately surrounding theextrusion 58. By holding the engagement of the plunger and contact tothis centrally disposed area, I insure to a high degree the provision ofa true double break, wherein both contact arms 60 leave the contactelements 50 simultaneously, so as to break the circuit at both sides ofthe bridging contact 54 at the same time. This, as is known in thetrade, is an arrangement which is sought after but often not fullyachieved, and it has been found in practice that the constructionillustrated and described tends to produce the desired simultaneousdouble break where ordinarily said double break would not be fullyachieved, particularly in View of the lateral pressures against theplunger for reasons given previously in this description.

Designated at 74 is a flat spacer washer of electrically insulativefibre or the like, with the plunger freely sliding in the center openingof said Washer. The washer 74 seats in the forward end of the body It),flush with the front end surface of said body. The stationary contactsare engaged directly against the washer, so as to be held in properposition, said stationary contacts being, in effect, fixedly clampedbetween the washer and the bottom surfaces of the depressions 4t} asshown in FIG- URE 8.

Further, as will be noted from FIGURE 6, the washer serves as a stoppermitting forward movement of the plunger beyond its normal, extendedposition shown in FIGURE 6, due to the engagement of the lugs 66 againstthe washer. Lugs 66, it may be noted, extend into the guide grooves 38,with the contact arms 69 also extending into said guide grooves, thus tohold the plunger, movable contact, and body against relative rotationalmovement.

Considering now the construction of the snap-in cover 74, this includesa shallowly dished plate member 76 centrally apertured for slidablemovement of the plunger therein, the plate member having an underlyingperipheral lip 78 formed with an annular series of uniformly spacedspring fingers ht slightly bent outwardly intermediate their ends asshown in FIGURE 6. Any two of the spring fingers can be bent under theshoulders 22 in the manner as shown at 24 in FIGURE 9, and thisrepresents an appreciable advance over conventional assembly methods ashereinbefore practiced in the art. Ordinarily, in a switch of this type,the spring fingers have not been employed for the purpose of assemblingthe body with the cover. Rather, separate pieces, either metallic orotherwise, have been required to accomplish this desirable objective. Inthe present instance, all the parts are held assembled between aone-piece phenolic body and a one-piece snap-in cover, thus reducing toa marked degree the number of parts required, while at the same timesimplifying assembly operations.

In assembly of the device, one would first insert the spring, then themovable contact, and then the stationary contacts. The plunger wouldthen be positioned upon the movable contact, after which the washer isapplied, followed by the cover, after which two of the fingers are bentunder the shoulders 22.

This completes the assembly of the switch, and the switch is readilyinstalled by snapping the same into a suitable opening of the panel ofthe refrigerator or other supporting structure, not shown. Either priorto or after installation of the switch, leads, not shown, are connectedto the terminals through the use of conventional push-on connectorscrimped or otherwise secured to the leads.

Connectors of the character described generally have rolled side edges,and in order to facilitate the application of said connectors withoutinterference from the body, I provide shallow side grooves 82 extendinglongitudinally of the body over the full length of the reduced portion14 thereof. These grooves accommodate the rolled edge portions of thepush-on connectors, so as to provide clearance for said connectors.

It may be noted that by reason of the illustrated arrangement, thereduced end portion 14 defines a wide, thick insulation barrier betweenthe terminals 46, which are ordinarily disposed in exposed positionsprojecting beyond the rear extremity of the body.

Further, the construction permits the stationary contacts to be muchshorter in length than is ordinarily the case, and this represents aconsiderable saving, in quantity production, of the metal used informing said contacts. Still further, the construction reduces the overall length of the portion of the switch that is disposed interiorly ofthe supporting panel of the refrigerator or other appliance, while stillachieving maximum normal projection of the plunger in relation to saidoverall length. Heretofore, the overall length of the device has beenincreased by the extent of the projection of the tabtype terminalsbeyond the rear end of the body.

It is believed apparent that the invention is not necessarily confinedto the specific use or uses thereof described above, since it may beutilized for any purpose to which it may be suited. Nor is the inventionto be necessarily limited to the specific construction illustrated anddescribed, since such construction is only intended to be illustrativeof the principles of operation and the means presently devised to carryout said principles, it being considered that the invention comprehendsany changes in construction that may be permitted within the scope ofthe appended claims.

I claim:

1. A plunger switch of the type designed to snap into a mounting hole ofan associated supporting structure, comprising: a body of molded,one-piece, dielectric construction formed as a cupped member open at oneend thereof; a centrally apertured cover for the open end of the bodyalso having a one-piece construction and including in its peripheralarea a series of spring fingers at least two of which are clinched intounderlying relation to portions of the body in direct contact with saidportions inwardly of the body circumference, the remaining fingers beingbowed outwardly to snap into said mounting hole; a plunger slidablymounted in and projecting out of the aperture of the cover; a. pair ofstationary contacts mounted in and having terminals projectingexteriorly of the body; a movable contact mounted for movement with theplunger and including contact surfaces, shiftable into and out ofengagement with the stationary contacts responsive to movement of theplunger between opposite extreme positions thereof; and a compressionspring seated in the body and engaging the movable contact, said springexerting a resilient, yielding pressure against the movable contact in adirection to extend the plunger from the body and shift the movablecontact into engagement with the stationary con tacts.

2. A plunger switch of the type intended to snap into a mounting hole ofan associated supporting structure, comprising: a body of molded,one-piece, dielectric construction formed as a cupped member open at oneend thereof, said body having angularly spaced external shouldersdisposed inwardly of the circumference of the body and faced toward therear end thereof; a centrally apertured cover for the open end of thebody also having a one-piece construction and including in itsperipheral area an annular series of spring fingers of identical lengthand outer configuration, said fingers being uniformly angularly spacedabout the entire circumference of the body, two at least of the fingersbeing clinched into underlying relation to said shoulders in directengagement therewith with the remaining fingers being bowed outwardly tosnap into said mounting hole; a plunger slidably mounted in andprojecting out of the aperture of the cover; a pair of stationarycontacts mounted in and having terminals projecting exteriorly of thebody; a movable contact mounted for movement with the plunger, saidmovable contact including contact surfaces shiftable into and out ofengagement with the stationary contacts responsive to operation of theplunger between opposite extreme positions thereof; and a compressionspring seated in the body and engaging the movable contact, said springexerting a resilient, yielding pressure against the movable contact in adirection to extend the plunger from the body and shift the movablecontact into engagement with the stationary contacts.

3. A plunger switch of the type intended to snap 7 into a mounting holeof an associated supporting structure, comprising: a body of molded,one-piece, dielectric construction formed as a cupped member open at oneend, said body being formed with a pair of diametrically opposedexternal shoulders faced toward the rear end thereof, the body havingabutments extending at opposite sides of each shoulder; a one-piececover including a flat, circular plate member having a central aperture,an annular lip underlying the periphery of the plate member, and anannular series of spring fingers identical to one another in length andouter configuration, said fingers depending from the lip and beinguniformly angularly spaced about the entire circumference of the body inpairs in which the fingers of each pair are arranged diametricallyopposite each other, each finger of a selected one of said pairs beingclinched into underlying relation to a shoulder between the abutmentsassociated with said shoulder, the remaining fingers being bowed out-'wardly to snap into said mounting hole; a plunger slidably mounted inand projecting out of the aperture of the plate member; a pair ofstationary contacts mounted in and having terminals projectingexteriorly of the body; a movable contact mounted for movement with theplunger, said movable contact including contact surfaces shiftable intoand out of engagement with the stationary contacts, responsive tooperation of the plunger between opposite extreme positions thereof; anda compression spring seated in the body and engaging the movablecontact, said spring exerting a resilient, yielding pressure against themovable contact in a direction to extend the: plunger from the body andshift said contact surfaces of the movable contact into engagement withthe stationary contacts.

' 4, A plunger switch of a type intended to snap into a mounting hole ofan associated structure, comprising: a body of molded, one-piece,dielectric construction formed as a cuppedv member having a circular,openlfront end and having a rear end portion formed with diametri callyopposed recesses extending to the rear extremity of the body from alocation intermediate the ends thereof, said recesses having end wallsat said location, said recesses opening upon the rear extremity of thebody; a cover for the open end of the body secured to the body andhaving a central aperture, said cover including means for snapping thesame into said mounting hole; a plunger slidably mounted in andprojecting out of the aperture of the cover; a pair of stationarycontacts mounted in the body and having rear end portions extending intothe recesses through the end walls to provide a pair of terminals forthe switch, said contacts being confined wholly within the circular areadefined by said front end of the body, said contacts terminating withinthe recesses short of the rear extremity of the body to locate thereduced portion of the body as an insulation barrier therebetween; amovable contact mounted for movement with the plunger, said movablecontact including contact surfaces shiftable into and out of engagementwith the stationary contacts responsive to operation of the plungerbetween opposite extreme positions; and a compression spring seated inthe body and engaging the movable contact, said spring exerting aresilient, yielding pressure against the movable contact in a directionto extend the plunger from the body and shift said contact surfaces ofthe movable contact into engagement with the stationary contacts.

5. A plunger switch of a type intended to snap into a mounting hole ofan associated supporting structure, comprising: a body of molded,one-piece, dielectric construction formed as a cupped member having anopen front end and having a rear end portion formed with diametricallyopposed recesses extending to the rear extremity of the body from alocation intermediate at the ends thereof, said recesses having endwalls at said location; a cover for the open end of the body secured tothe body and having a central aperture, said cover including m ans forsnapping the same into said mounting hole; a plunger slidably mounted inand projecting out of the aperture of the cover; a pair of stationarycontacts having front end portions extending longitudinally of andwithin the body, arms projecting laterally from one side of the frontend portions adjacent to and in a direction parallel to the generalplane of the cover, contact elements depending from said arms, and rearend portions extending through said end walls into the recesses toprovide a pair of terminals for the switch, said contacts terminatingwithin the recesses short of the rear extremity of the body to locatethe reduced portion of the body as an insulation barrier therebetween; amovable contact mounted for movement with the plunger, said movablecontact including contact surfaces shiftable into and out of engagementwith said contact elements in response to operation of the plungerbetween opposite extreme positions thereof; and a compression springseated in the body and engaging the movable contact, said springexerting a resilient, yielding pressure against the movable contact in adirection to extend the plunger from the body and shift said contactsurfaces of the movable contact into engagement with the contactelements of the stationary contacts.

6. A plunger switch of a type intended to snap into a mounting hole ofan associated supporting structure, comprising: a body of molded,one-piece, dielectric construction formed as a cupped member having anopen front end and having a rear end portion formed with diametricallyopposed recesses extending to the rear extremity of the body from alocation intermediate at the ends thereof, said recesses having endwalls at said location; a cover for the open end of the body secured tothe body and having a central aperture, said cover including means forsnapping the same into said mounting hole; a plunger slidably mounted inand projecting out of the aperture of the cover; a pair of stationarycontacts having straight, flat body portions extending longitudinally ofand within the body, arms projecting laterally from one end of therespective body portions angularly to the planes of said body portions,said arms extending from one side of said body portions in a directionparallel to the general plane of the cover, contact elements dependingfrom said arms, said body portions at their other ends extending throughsaid end walls of the recesses to provide a pair of terminals for theswitch, said terminals terminating within the recesses short of the rearextremity of the body and wholly within the circumference of the body tolocate the reduced portion of the body as an insulation barriertherebetween; a movable contact mounted for movement with the plunger,said movable contact including contact surfaces shiftable into and outof engagement with said contact elements in response to operation of aplunger between opposite extreme positions thereof; and

. a compression spring seated in the body and engaging the movablecontact, said spring exerting a resilient, yielding pressure against themovable contact in a direction to extend the plunger from the body andshift said contact surfaces of the movable contact into engage ment withthe contact elements of the stationary contacts.

References Cited by the Examiner UNITED STATES PATENTS 2,605,375 7/52Ellithorpe 200-159 2,712,047 6/55 Herterick 200-159 2,886,674 5/59SpiCer 200-159 2,899,511 8/59 Fraser ZOO-61.81 2,903,540 9/59 Gloviak200-168 X 2,969,443 1/61 Barden 200-168 2,994,750 8/61 Raab 200-159FOREIGN PATENTS 597,560 1/48 Great Britain.

BERNARD A. GILHEANY, Primary Examiner. ROBERT K. SCHAEFER, Examiner.

1. A PLUNGER SWITCH OF THE TYPE DESIGNED TO SNAP INTO A MOUNTING HOLE OFAN ASSOCIATED SUPPORTING STRUCTURE, COMPRISING: A BODY OF MOLDED,ONE-PIECE, DIELECTRIC CONSTRUCTION FORMED AS A CUPPED MEMBER OPEN AT ONEEND THEREOF; A CENTRALLY APERTURED COVER FOR THE OPEN END OF THE BODYALSO HAVING A ONE-PIECE CONSTRUCTION AND INCLUDING IN ITS PERIPHERALAREA A SERIES OF SPRING FINGERS AT LEAST TWO OF WHICH ARE CLINCHED INTOUNDERLYING RELATION TO PORTIONS OF THE BODY IN DIRECT CONTACT WITH SAIDPORTIONS INWARDLY OF THE BODY CIRCUMFERENCE, THE REMAINING FINGERS BEINGBOWED OUTWARDLY TO SNAP INTO SAID MOUNTING HOLE; A PLUNGER SLIDABLYMOUNTED IN AND PROJECTING OUT OF THE APERTURE OF THE COVER; A PAIR OFSTATIONARY CONTACTS MOUNTED IN AND HAVING TERMINALS PRO-